<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>事件</title>
	<style>
		#box{
			width: 200px;
			height: 200px;
			background: red;
		}
	</style>
	<script>
		window.onload= function () {
			
			box = document.getElementById('box');

			btn = document.getElementsByClassName('btn')

			// box.onmouseover= function () {
			// 	box.style.width= "400px";
			// 	box.style.height= "400px";
			// }

			btn[0].ondblclick = function () {
				box.style.width= "400px";
				box.style.height= "400px";
			}
		}
		function run() {
			alert(5656)
		}
	</script>
</head>
<body>
	<p id="box">学并思</p>
	<input type="button" value="变大" class="btn">
	<a href="" onmouseover="run()">sdfsdf</a>
</body>
</html>